| Tropical storm (SSHS) | |
|---|---|
| Tropical Storm Allison near landfall | |
| Formed | June 24, 1989 |
| Dissipated | June 28, 1989 |
| Highest winds | 1-minute sustained: 50 mph (85 km/h) |
| Lowest pressure | 999 mbar (hPa; 29.5 inHg) |
| Fatalities | 11 direct |
| Damage | $560 million (1989 USD) |
| Areas affected | East Texas, Louisiana |
| Part of the 1989 Atlantic hurricane season | |
Tropical Storm Allison was a tropical cyclone that produced severe flooding in the southern United States. The second tropical cyclone and the first named storm of the 1989 Atlantic hurricane season, Allison formed on June 24 in the northwestern Gulf of Mexico. Development of Allison was a result of the interaction of a tropical wave and the remnants of Pacific hurricane Hurricane Cosme. It moved south and became a tropical storm on June 26. By June 27, Allison made landfall near Freeport, Texas. Allison quickly weakened to a tropical depression later that day, and transitioned into an extratropical cyclone on the following day.
The storm caused heavy rainfall, amounting to 30 in (760 mm) in some places. In total, 11 fatalities resulted from the storm, as well as $560 million (1989 USD, $992 million 2012 USD) in damage.
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Three meteorological phenomena combined to produce Tropical Storm Allison. First, Hurricane Cosme moved northward through Mexico in response to a strong mid to upper-level ridge. Its remnants entered the Gulf of Mexico on June 22, when a westward moving tropical wave reached the area. Finally, a strong anticyclone over the Gulf allowed for the disturbed area to organize into Tropical Depression Two in the western Gulf of Mexico on June 24.[1]
The depression continued to organize as it drifted to the north, and became Tropical Storm Allison on June 26 off the Texas coast.[1] A ridge to Allison's north weakened in response to an approaching frontal trough, and the tropical storm accelerated to the north. Allison reached a peak of 50 mph (80 km/h) winds just before hitting near Freeport, Texas on June 27. It turned to the northeast with the front, weakened to a tropical depression on June 27, and became extratropical on June 28.[2]
The frontal trough outran the system, and the building ridge to Allison's north forced the extratropical depression turned to the south and southwest. After executing a cyclonic loop over Texas, the ridge to the north began to erode, allowing Allison to track northeast and out of the state. Its circulation dissipated on July 1, but the remnants retained some organization, and continued to the northeast. On July 3 and July 4, the shortwave that influenced the remnants of Allison accelerated ahead of the storm, causing Allison to become stationary over the borders of Kentucky, Illinois, and Indiana. A second shortwave trough brought the remnants of Allison southward into Alabama. It turned to the northwest, and the remnants of Allison became unidentifiable over Arkansas on July 7.[2]
In preparation for Tropical Storm Allison, a tropical storm watch was issued on June 24 for Baffin Bay, Texas to Morgan City, Louisiana. By June 26, this alert was upgraded to a tropical storm warning. All advisories were discontinued the next day.[3]
While Allison's winds weren't overly strong, it caused tremendous flooding in Texas and Louisiana, with 20 to 25 in (510 to 630 mm) in of rain occurring in some locations. The local hardest hit by the flooding was Winnfield, Louisiana, which experienced almost 30 in (760 mm) of rain from June 26 to July 1.[4][5]
Rainfall from the storm extended eastward into the Mid-Atlantic States, producing flooding.[6] In Delaware, the rainfall led to record breaking discharge rates at three gauging stations, while one-third of the state's gauging stations reported significant discharges.[7]
13.9 in (350 mm) of rain fell at a site in Arkansas, the highest rainfall total from a tropical cyclone in the state.[8]
Eleven people were reported killed from the storm. Three deaths occurred in Texas, five in Mississippi and three in Louisiana. Two teenage boys were killed when their raft got sucked into a drainage pipe from the runoff of Allison in Beaumont, Texas. An eighteen-year-old was killed in Harris County, Texas from drowning during a swim. The eight final deaths in Louisiana and Mississippi were by drowning. The extreme flooding in turn led to heavy damage, amounting to around $560 million (1989 USD, $992 million 2012 USD).[9]
